1. Field of the Invention
The present invention relates to a system and a method for an automatic set-up and tear down of switched circuits based on the monitoring and/or forecasting of the ingress packet traffic in nodes of a telecommunications network.
2. Description of the Related Art
TDM (Time Division Multiplexing) transport networks (e.g. SDH) have been basically designed for voice and leased line services. In the last years many network operators have largely deployed SDH transport platforms in both long haul and metropolitan/regional networks. However, today it is widely recognized that traffic on transport networks will be progressively dominated by data traffic (especially Internet-based), with respect to traditional voice traffic, due to a progressive migration of many applications and services over the Internet Protocol (IP), and thanks to the introduction of high-speed access technology. The introduction of WDM (Wavelength Division Multiplexing) or DWDM (Dense Wavelength Division Multiplexing) optical point-to-point systems is already providing high capacity links in order to cope with the growing of the traffic demands. On the other hand, the statistical characteristics of this growing data traffic (especially IP traffic) are rather different from those of traditional voice traffic. As a whole, IP traffic is not easily predictable and stable as the traditional voice traffic. In turn, IP traffic may show unpredictable traffic bursts. Consequently, main requirements for new-generation transport networks include flexibility and ability to react to traffic demand changes with time. Another key issue relates to the fact that even though the data traffic (especially Internet traffic) is becoming dominant, it does not generate revenue as do valuable voice services. Practically, this means that if a network was upgraded by adding bandwidth and expanding infrastructure in proportion to the amount of data traffic increase, the revenues would be smaller than the overall costs. For this reasons, network operators are seeking both to accommodate increasing bandwidth demands for data traffic and to dynamically provide optical connections, trying to make an optimal use of the available network resources and saving operating costs. For example, simply dimensioning a transport network to cope with data traffic bursts could be inefficient and expensive.
Traffic engineering (TE) is the process to control traffic flows in a network in order to optimize resource use and network performance. Practically, this means choosing routes taking into account traffic load, network state, and user requirements such as Quality of Service (QoS) or bandwidth, and moving traffic from more congested paths to less congested ones.
In order to achieve TE in an Internet network context, the Internet Engineering Task Force (IETF) has introduced MPLS (Multi Protocol Label Switching). The MPLS scheme is based on the encapsulation of IP packets into labeled packets that are forwarded in a MPLS domain along a virtual connection called label switched path (LSP). MPLS routers are called label switched routers (LSRs), and the LSRs at the ingress and egress of a MPLS domain are called edge LSRs (E-LSRs). Each LSP can be set up at the ingress LSR by means of ordered control before packet forwarding. This LSP can be forced to follow a route that is calculated a priori thanks to the explicit routing function. Moreover, MPLS allows the possibility to reserve network resources on a specific path by means of suitable signaling protocols. In particular, each LSP can be set up, torn down, rerouted if needed, and modified by means of the variation of some of its attributes. Furthermore, preemption mechanisms on LSPs can also be used in order to favor higher-priority data flows at the expense of lower-priority ones, while avoiding congestion in the network.
To extend the features of the MPLS technique, a generalized version of the same has also been proposed, known as GMPLS. GMPLS encompasses time-division (e.g. SONET/SDH, PDH, G.709), wavelength, and spatial switching (e.g. incoming port or fiber to outgoing port or fiber). The establishment of LSPs that span only Packet Switch Capable (PSC) or Layer-2 Switch Capable (L2SC) interfaces is defined for the MPLS and/or MPLS-TE control planes. GMPLS extends these control planes to support all the interfaces (i.e. layers): Packet Switch Capable (PSC) interfaces, Layer-2 Switch Capable (L2SC) interfaces, Time-Division Multiplex Capable (TDM) interfaces, λ-Switch Capable (LSC) interfaces, Fiber-Switch Capable (FSC) interfaces. According to current standards, the GMPLS control plane can support three models: overlay, augmented and a peer (integrated) models. These models are differentiated based on the amount of routing/topological information exchanged between the layer networks.
P. Iovanna, R. Sabella, M. Settembre, in the article “A Traffic Engineering System for Multilayer Networks Based on the GMPLS Paradigm”, IEEE Network, March-April 2003, pag. 28-35, propose a traffic engineering system able to dynamically react to traffic changes while at the same time fulfilling QoS requirements for different classes of service. The solution by the authors consists of a hybrid routing approach, based on both offline methods and online methods, and a bandwidth management system that handles priority, preemption mechanisms, and traffic rerouting in order to concurrently accommodate the largest amount of traffic and fulfill QoS requirements. More specifically, the TE system invokes an offline procedure to achieve global optimization of path calculation, according to an expected traffic matrix, while invoking an online routing procedure to dynamically accommodate, sequentially, actual traffic requests, allowing reaction to traffic changes. The building blocks of the TE system are: a path provisioning module, a dynamic provisioning module, a bandwidth engineering module. The path provisioning module calculates offline the routes for all foreseen connections, according to a traffic matrix that describes the traffic relationships between each network node pair, on the basis of the physical topology of the network and information about network resources (e.g., presence of wavelength conversion inside optical cross connects, link capacity). The dynamic routing module evaluates the route for a single LSP request at a time, expressed in terms of source and destination nodes and bandwidth requirements. Basically, the dynamic routing algorithm finds a route aimed at better utilizing network resources by using less congested paths instead of shortest, but heavily loaded paths. The TE system is based on elastic use of bandwidth: the bandwidth can be temporary released by higher priority LPSs and put at disposal of all the lower priority LPSs. This can be done provided that the bandwidth is immediately given back to high priority traffic as soon as needed. When a higher priority LSP requires more bandwidth and at least one link on its path is congested, the bandwidth engineering module is invoked to make the required bandwidth available. The bandwidth engineering module can be represented by a preemption module that tears down all the LSPs whose priority level is lower than that of the LSP to be accommodated.
A. Gençata and B. Mukherjee, in the article “Virtual-Topology Adaptation for WDM Mesh Networks Under Dynamic Traffic”, IEEE/ACM Transactions on Networking, Vol. 11, No. 2, April 2003, pag. 236-247, propose an approach for the virtual-topology reconfiguration problem for a WDM based optical wide-area mesh network under dynamic traffic demand. The key idea of the authors' approach is to adapt the underlying optical connectivity by measuring the actual traffic load on lightpaths continuously (periodically based on a measurement period), and reacting promptly to the load imbalances caused by fluctuations on the traffic, by either adding or deleting one or more lightpaths at a time. When a load imbalance is encountered, it is corrected either by tearing down a lightpath that is lightly loaded or by setting up a new lightpath when congestion occurs.
U.S. patent application No. 2003/0067880 discloses a system and a method of implementing Routing Stability-Based Integrated Traffic Engineering for use in an MPLS/optical network. Incoming network traffic is classified as high priority, which can tolerate limited rerouting. In accordance with one embodiment, high priority traffic trunks are mapped onto direct light channels (or LSPs) and rerouted only in the event of a light channel tear down due to poor traffic utilization. According to the applicant of '880 patent application, a direct light channel, or LSP, is one that comprises a direct optical connection between an ingress/egress node pair via one or more OXCs. Low priority traffic trunks are mapped onto direct light channels if available; otherwise, they are mapped onto multi-hop LSPs with appropriate optical/electrical/optical conversions at the edge nodes serving as intermediate hops. According to the applicant of '880 patent application, a multi-hop light channel, or LSP, is one that constitutes more than one light channel and hence comprises an optical connection between an ingress/egress node pair via one or more OXCs and one or more edge nodes other than the ingress/egress nodes. The optical/electrical/optical conversions at the intermediate nodes may introduce packet delays for the traffic mapped onto multi-hop LSPs. Each such low priority traffic trunk is associated with a rerouting timer that is set at the time of rerouting, so as to prevent another rerouting of the trunk until the timer expires.